The apparent molar volume, V-phi,2(o), of glycine, alanine, alpha-amino-n-butyric acid, valine and leucine have been determined in aqueous solutions of 0.25, 0.5 and 1.0 mol . dm(-3) magnesium sulfate, and the partial specific volume from density measurements at 298.15 K. These data have been used to calculate the infinite dilution apparent molar volume, V-2,m(o), group contribution of amino acids and partialmolar volume of transfer, Delta(tr) V-2,m(o), from water to aqueous magnesium sulfate solutions. The linear correlation of V-2,m(o) for a homologous series of amino acids has been utilized to calculate the contributions of charged end groups (NH3+, COO-), CH2- groups and other alkyl chains of amino acids to V-2,m(o). The results for Delta(tr) V-2,m(o) of amino acids from water to aqueous magnesium sulfate solutions have been interpreted in terms of ion-ion, ion-polar, hydrophilic-hydrophilic and hydrophobic-hydrophobic group interactions. The values of the standard partial molar volume of transfer for the amino acids with different hydrophobic contents, from water to aqueous MgSO4 are in general positive, indicating the predominance of the interactions of zwitterionic/hydrophilic groups of amino acids with ions of the salt. The hydration number decreases with increasing concentration of salt. The number of water molecules hydrated to amino acids decreases, further strengthening the predominance of ionic/hydrophilic interactions in this system.